A nearly daily routine in most residences and places of business is the waiting for, checking for, retrieval of mail once delivered to one's mail receptacle and, in some cases, walking back from the mail receptacle empty handed. Existing mailbox mail detection systems detect the opening or closing of a mailbox by affixing a detector to the mailbox door. Such systems are inherently susceptible to false positives that can occur when the mailbox is opened, closed, or otherwise disturbed, but no mail in fact is deposited therein. Such systems are also susceptible to false negatives whenever the mailbox utilizes an alternative mode of mail deposition, such as a letter slot that permits a letter to be slipped in the mailbox without the door being opened. Furthermore, such systems are unsuitable for cluster mailboxes that are common in apartment complexes, post offices, and neighborhoods where the mailman opens a single door to multiple mailboxes at once. The United States Postal Service prefers to establish the most efficient mode of delivery in new residential developments and is now requiring most new developments to install centralized mail delivery installations for residential communities, known as Neighborhood Delivery Centers or cluster mailboxes. An example of such a centralized mail delivery installation is shown in FIG. 1.
Other mail detection systems detect changes in the weight of the load supported by the mailbox, assuming that mail deposited therein will increase the weight pushing against the floor of the mailbox, or in other cases, assuming that the combined weight of the mailbox and its contents will detectably vary with each item of mail added to the mailbox. These systems are disadvantageous because they require the installation of a scale or other means for measuring weight, either in a custom mailbox or a preexisting mailbox, which is a relatively expensive undertaking both in the initial installation, and because they require regular maintenance due to the sensitivity of the scales, which need regular repairs and calibration. Furthermore, changes in climate may change the calibration of scales which can cause false detection to occur, requiring ongoing recalibration. Scales also fail whenever mail is stuffed or crammed into mailboxes; for example, when larger envelopes are folded and/or wedged into the box and then become effectively “suspended” by the friction of the envelope against the walls of the box so that their mass is not fully applied to the scale. Furthermore, many scales are unreliable for detecting very light objects, and most weight-detection systems fail to reliably discern small fluctuations in weight such as that contributed by a paper letter, postcard, or other low-weight mail. This is especially the case when a very light object is added to a heavy mailbox or a mailbox that already contains a relatively heavy load.
Others have used cameras positioned inside a mailbox to detect mail. However, this approach may cause privacy issues because such information could be targeted by cyber criminals. Furthermore, detecting change in images requires significant computational power, which may result in a decreased operational time for a battery powered device. Still others have positioned security cameras to detect motion around their mailbox, but this again fails to reliably indicate whether mail has actually been added or removed from the mailbox enclosure. Nearby wildlife, for example, may provide false positives. Still others have relied upon detecting changes in light intensity inside a mailbox enclosure to detect mail as the deposited mail is typically a different color and reflects light differently from the interior of a mailbox. However, this method also fails to account for changes associated with sunlight and nearby artificial lighting that can penetrate gaps in the mailbox enclosure and cause unreliable results.
Armstrong in Canada Pat. No. CA2016/050214 requires a tray-like system be installed to cover nearly the entire floor of the mailbox. This method is bulky and cannot detect the presence of additional mail being added if the original mail already occupies the entire floor of the mailbox.
Others use ultrasonic sensors as a ranging device to detect an object, such as mail, placed between the ultrasonic sensor and another sensor or reflector. Such an approach in effect acts as an open or closed circuit and is limited insofar as it cannot reliably detect small pieces of mail, such as a letter or postcard lying flat on the floor of the mailbox or along the side of the mailbox wall, because the cross section of the mail relative to the direction of the ultrasonic sensor is so small that it is lost in the clutter of the mailbox floor or walls. Others have used multiple ultrasonic sensors, but this adds to the complexity of the system and requires additional installation of either bulky devices or multiple sensors separated throughout the mailbox.
One approach for detecting the delivery of mail to a mailbox enclosure is disclosed in U.S. Pat. No. 4,633,236 A to Buhl issued Dec. 30, 1986, where an ultrasonic sensor is installed on one end of the enclosure and a reflector is installed on the other end to develop a predetermined path for the presence of mail to close the circuit or the removal of mail to open the circuit. However, this method is ill suited to reliably detect small parcels, such as postcards lying flat along the vertical sides of the enclosure.
Another approach disclosed in U.S. Pat. No. 6,462,659 B1 to Schuette issued Aug. 8, 2002 discusses that unspecified variations in received acoustic signals, such as a break in ultrasonic communications, can be used to detect mail within a mail receptacle. However, this method is unable to detect small parcels of mail (e.g., a postcard) lying flat on every possible surface of a mailbox enclosure, without ultrasonic sensors dispersed along a minimum of three axis. Such a setup would be burdensome to install and more expensive compared to installing a single ultrasonic sensor in a mailbox receptacle.
Japanese Pat. No. JP5845142B2 to Suzuki Hiroo relies upon ultrasound signals being blocked or the path broken. As previously mentioned, such an approach is unable to reliably detect small parcel of mail, or mail oriented in particular directions or located in particular areas.
Others have used ultrasound transceivers as they are primary intended to operate as ranging devices to detect mail. In Canadian Pat. No. CN203619290U to Li Yongqui, a baseline of the time of flight of the signal to bounce back is performed on an empty mailbox enclosure. This method measures the distance between the sensor and the nearest object, in this case the opposite side of the enclosure. When mail is inserted into the mailbox enclosure the time of flight is reduced and mail is detected. However, this method only works for large parcels such as boxes and is ill suited for small mail parcels such as, for example, a postcard lying flat on the bottom of the mailbox enclosure. A postcard's cross section in such a scenario may be lost in the clutter of the returning signal depending on its orientation and positioning. Even when the ultrasound sensor is placed as close as possible to the floor of the mailbox enclosure reliability is low because of many false positives associated with increased clutter noise caused by the bottom of the mailbox enclosure.
U.S. Pat. No. 7,786,862 B1 to Campbell issued Aug. 31, 2010 requires the sensor to be operated nearly continuously to sense motion. This is not a practical solution as the power supply is typically portable in nature (e.g., batteries). Such a portable power supply would be quickly exhausted upon such continuous use. Attachment to a continuous power supply, such as a utility line, would add significant complexity and cost for manufacturing and installation.
Therefore, what is needed is a system and method for reliably detecting the addition or removal of various size physical objects. The present invention is a system and method for reliably detecting the addition or removal or various size physical objects.
An ultrasonic sensor may be placed within a receptacle. The ultrasonic sensor may emit a burst of ultrasonic waves which may be reflected off the surfaces of the receptacle as well as any object(s) located therein. The sensor may be calibrated by emitting a burst of ultrasonic waves when the receptacle is known to be empty and receiving the echoes of the waves from the initial burst over a period of time. The ultrasound sensor may detect the amplitude of echoed waves from the initial burst and record the received data over multiple echoes, such as until the signals can no longer be heard above the noise floor. A microcontroller in communication with the ultrasound sensor may calculate the rate of decay of the amplitude associated with the original burst of ultrasound energy to established a baseline decay rate. Additional calibration may be performed with objects in the receptacle.
The ultrasound sensor may selectively emit one or more subsequent bursts of ultrasonic waves and detect the amplitude of the echoed waves from each of the subsequent bursts over a second period of time. The received data may be processed by the microcontroller to determine a test decay rate for each subsequent burst. The respective test decay rate may be compared against the baseline decay rate to determine if one or more objects have been added or removed from the receptacle. In exemplary embodiments, the determination that an object has been added to the receptacle is made if the test decay rate is larger than the baseline decay rate by a predetermined amount. If the test decay rate is not greater than the baseline decay rate by the predetermined amount, the test decay rate may be set as the new baseline decay rate.
In other exemplary embodiments, the determination that an object has been added to the receptacle is made by subtracting the baseline decay rate from the test decay rate to arrive at a first value. If the first value is greater than a predetermined amount, then a determination that an object has been added is made. If no such determination is made, the test decay rate is subtracted from the baseline decay rate to arrive at a second value. If the second value is greater than the predetermined amount, then a determination is made that an object was removed from the receptacle. However, if the second value is less than the predetermined amount the test decay rate may be set as the new baseline rate.
Such a system and method results in reliable detection of even small objects, such as but not limited to, the presence of a postcard lying flat on the bottom of a mailbox. Such a system and method could furthermore be utilized across multiple receptacle types, be capable of reliably detecting various size objects, require little to no modification to the receptacle, provide a small profile device which can operate for extended periods of time, and be installed easily by a non-handy person.
While several examples are given of the detection of mail or other objects in a mailbox, it is contemplated that the receptacle may be any closed compartment or area. Likewise, the detected object may be any size or shape object. For example, without limitation, the receptacle may be a room, lockbox, vault, drawer, and the like. Furthermore, while several examples are given of the use of ultrasonic energy and sensors, it is contemplated that other types of energy and related sensors which are capable of exciting molecules in an enclosure may be utilized. Such examples include, without limitation, lasers, x-rays, microwaves, and the like.
Further features and advantages of the devices and systems disclosed herein, as well as the structure and operation of various aspects of the present disclosure, are described in detail below with reference to the accompanying figures.